It's not uncommon to learn that some historic writer or poet or other creative was employed as a "clerk" and supported themselves, and their family, that way. Specific examples off the top of my head include Samuel Mathers, Franz Kafka, TS Eliot...
Surely they weren't working menial retail jobs—I'm fairly certain the concept of today's retail work wasn't even a thing until like the 1950s (though I could be wrong about that)!
So what were they doing, exactly? Did it actually pay well? Is there a modern day equivalent?
The easy thing to address is for your examples it's meant in the sense of office clerks, rather than store clerks. They would have been doing some kind of record keeping and/or paperwork.
We have this question earlier asking about Bob Cratchit, who is identified as a clerk in A Christmas Carol:
https://www.reddit.com/r/AskHistorians/comments/1i3c5x/how_good_of_a_job_did_bob_cratchit_have/
I should add the caveat that A Christmas Carol was published in 1843, but I didn't find any good posts about office work closer to the turn of the century, which would fit your examples much better.
Since you list T.S. Eliot, it might be worth noting he wrote The Confidential Clerk, where the titular clerk can be understood as a personal secretary:
https://archive.org/details/in.ernet.dli.2015.547673/page/5/mode/2up